Hi there,
I have an idea I'd like to bounce off people here. It relates to the
problem described here:
http://www.sqlalchemy.org/docs/05/session.html#unitofwork_contextual
The solution used there makes the assumption that each request will
happen in its own thread, and uses python's thread-local stuff to do
its magic.
I was wondering if it is not possible to do something that is local to
the current call-stack, instead of the current thread. I think there
are two issues here:
a) a general mechanism for remembering a call-local context
b) using it to provide a call-local sqlalchemy session
Now, I'm not sure yet how to do (b), but want to give an example of
(a) with a naive implementation to illustrate the idea. (Just note
this mechanism can be used for other important contextual info as
well, such as who the current user is, etc)
With the following code, I can call a method b.bar, passing it some
"context" (which is not part of the method's original signature).
b.bar calls a.foo in turn, also not passing it anything, but inside
A.foo, the context can be retrieved from the call stack. The only
overhead incurred is during this last step, and I don't think it is
much. (Implementation of CC is at the bottom.)
Any thoughts?
class A(object):
def foo(self):
print CC.get_context() #CC here is assumed to be a class,
on which a class method is
# called to get
the current "context", which may be our session
# but I think it
can be used for more things than just the session
class B(object):
a = A()
def bar(self, arg):
print arg
self.a.foo()
b = B()
CC(b.bar, 'context stuff - a session or a dict?', 'some argument for
bar()')
#---------------------
# CC (should be before the examples above if you want to run it)
#
import inspect
class CC(object):
def __init__(self, callable, context, *args, **kwargs):
self.callable = callable
self.context = context
self.callable(*args, **kwargs)
@classmethod
def get_context(cls):
context = None
found = False
f = inspect.currentframe()
while not found and f.f_back:
theSelf = f.f_locals.get('self', None)
if theSelf.__class__ is cls:
context = theSelf.context
found = True
nextF = f.f_back
del f
f = nextF
return context
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